Automotive vehicles are commonly equipped with various signal communication devices such as audio radios for receiving broadcast radio frequency (RF) signals, processing the RF signals, and broadcasting audio information to passengers in the vehicle. Satellite digital audio radio (SDAR) services have become available that offer digital radio service covering a large geographic area, such as North America. Currently, a couple of satellite-based digital audio radio services are available in North America. These SDAR services are referred to as Sirius satellite radio which employs three satellites in elliptical orbit and XM satellite radio which employs two satellites in geo-stationary orbit. Both services receive uplinked programming which, in turn, is rebroadcast directly to digital radios that subscribe to the service. Each subscriber to the SDAR service generally includes a digital radio having a receiver and one or more antennas for receiving the digital broadcast.
In the SDAR services system, the radio receivers are generally programmed to receive and decode the digital data signals, which typically include many channels of digital audio. In addition to broadcasting the encoded digital quality audio signals, the SDAR service may also transmit data that may be used for various other applications. The broadcast signals may include information for advertising, informing the driver of warranty issues, providing information about the broadcast audio information, and providing news, sports, and entertainment broadcasting. Thus, the digital broadcasts may be employed for any of a number of satellite audio radio, satellite television, satellite Internet, and various other consumer services.
In vehicles equipped with the SDAR service, each vehicle generally includes one or more antennas for receiving the satellite digital broadcast. One example of an antenna arrangement includes one or more antennas mounted in the outside rearview mirror housing(s) of the vehicle. Another antenna arrangement includes a thin phase network antenna having a plurality of antenna elements mounted on the roof of the vehicle. The SDAR antenna(s) may be mounted elsewhere in the vehicle.
As the antenna profiles for the SDAR services systems become smaller, performance of the antenna may be reduced. To regain this lost performance, multiple small directional antennas may be used that compliment each other. This type of antenna system relies on switching to the best antenna source for the signal reception. Another option is to combine the antenna with beam steering electronics. For low cost application, a switched diversity antenna may be employed. In doing so, the RF receiver controls which antenna to use by detecting the presence of a desired signal.
A system that uses only one type of signal detection (i.e., signal quality detection in the receiver) generally must switch to another antenna when the signal is lost. This switching approach is generally referred to as blind switching because there is generally no information considered from the other antenna(s) to indicate the probability of success in finding a better desired signal. When the antenna employed has a weak signal, if the receiver switches to another antenna that exhibits a poorer quality signal or no signal, reduced antenna performance may be experienced. This may result in a loss of information which, in an audio radio, can result in audio mute. Hence, the conventional blind switching technique requires the receiver to wait longer before switching and requires the receiver to quickly determine if the new antenna has a valid signal.
It is therefore desirable to provide for an antenna system that allows for selective control to achieve optimal signal reception from a plurality of transmission sources. In particular, it is desirable to provide for an antenna system that advantageously allows for enhanced selection of received signals for use on a mobile vehicle.